1. Field of the Invention
This invention relates to a splice closure assembly which will provide a sealed closure for splices in a fiber optic cable, and in one aspect to a splice closure which affords significant storage area for slack fiber upon interrupting a cable to make a branch splice in the cable.
2. Description of the Prior Art
Splice closures are commonplace for wire splices in electrically conductive telecommunication cables. Optical fiber cable splice closures differ in that excess fiber lengths should be provided for anticipated future rearrangements and future additions or changes in the splices and those lengths of fibers must be protected against breakage or bending which would affect transmission properties.
Optical fiber cables are supplied in many configurations and may be of composite constructions which also include electrical conductors. Each of these cables, however, is comprised of at least three functional elements, an outer sheath construction surrounding the optical or composite optical and electrical conductors, provision to withstand cable tension during either placement or when permanently installed, and multiple optical fibers or composite optical and electrical conductors. Optionally, a metallic shield, rodent protection, multiple sheath layers, hydroscopic filling compound, multiple dielectric strands, and the like may be provided. At each access location where it is necessary to remove a portion of the cable sheath, it is necessary to protect the optical fibers by a splice closure which restores mechanical and environmental protection for the cable. The splice closure protects the fibers from breakage or bend radii which would induce attenuation loss or signal interruption. A protective buffer tube surrounds each optical fiber or group of optical fibers, and is maintained between the cable sheath opening and a protective splice tray which stores the optical fiber splices and exposed unprotected optical fibers.
Excess optical fiber capacity is required for each spliced fiber and for unspliced fibers where only a percentage of the cabled optical fibers or fibers in a cable are spliced as in a branch splice. Installing uncut cables, i.e. unsevered optical fibers, in a splice closure improves network reliability by minimizing optical fiber discontinuities and avoiding unnecessary splices. In a location where it is necessary to interrupt an optical fiber and obtain access to the cable and the buffer tube with the selected optical fiber(s), it is necessary to sever and remove a portion of the sheath of the cable and gain access to the buffer tubes. A predetermined length of slack for buffer tubes of the main cable are then formed into loops to be placed in the splice closure. The buffer tube to which access is desired is selectively removed and the exposed fibers are drawn from the buffer tube and are formed into a loop or loops for storage in the splice tray with the selected fiber cut and spliced to the end of another fiber extending from the branch cable directed to a remote distributing site or other signal processing equipment. Sufficient slack in the buffer tubes and optical fibers from one buffer tube allows future splicing and the most network flexibility and would not require rebuilding the transmission line to affect additional or subsequent splices in the same area. Adequate storage for unsevered buffer tubes and severed buffer tubes is required.
In those instances where multiple optical fibers are contained within a single unsevered buffer tube, the branch cable splice may require splicing only a percentage of those fibers. This situation is accommodated by selectively removing a mid-slack length of buffer tube, installing both tube ends within a splice tray to house the spliced fibers, severing and splicing the required fibers, and coiling the unsevered, unprotected remaining fibers for storage within the splice tray.
Thus the present invention provides a fiber optic cable splice closure for branch line splices without interrupting the continuity of unspliced optical fibers in the same cable and to which no splice is made. The present invention is directed to a fiber optic cable splice closure for use in making branch splices to a transmission cable. The closure comprises basically a two-piece mechanical closure assembly including a base and cover and integrated cable termination hardware within the base for providing strain relief to the jacket of the cable assembly.
The closure of the present invention provides a strength member anchor for the strength member of the cables installed in the closure.
The present invention provides a splice holder for control and storage of the slack fibers which are spliced and buffer tube retainers to retain and store the uncut slack fibers in the closure in an environment to restrict damage thereto and afford protection therefor. The present invention provides a closure which is readily expanded by the addition of one or more adapter plates expanding the closure assembly capacity to accommodate a greater number of cables.
The features of the closure constructed according to the present invention are not present in the prior art closures. For example, the closure of U.S. Pat. No. 4,428,645 is not designed to accommodate a branch splice in a transmission cable. It is designed to enclose only butt splices between optical fibers in two cables, first cable 20 and second cable 21. Thus, the closure has limited utility. There is provision for slack cable storage but the cable sheath and shield are not removed for access to cable strain members and slack buffer tubes in a multi-fiber cable. There was no dedicated area to store slack unsevered protected optical fibers or a second storage area providing space for an installed splice tray to store slack severed optical fibers and splices therebetween. Each cable is required to pass through an orifice into the closure, and then to pass through openings 43 and 46 into separate storage areas and then through additional separate openings 25 and 26 into an organizer B. Such structure thereby preventing storage of unsevered fibers. The dedicated areas of the present invention are open, without transverse barriers for initially laying in loops of unsevered optical fibers of a transmission cable and loops of the selected fibers. Additional cables from or forming branch lines may terminate at the closure or run through the closure.
A prior closure of AT&T comprises a base and a closure cover. Two additional separate closure covers are used to seal and terminate the cables to the base. Hinged storage leafs are used to store the spliced fibers and the closure cover fits on the upper storage leaf. The base is not provided with a dedicated area free of transverse barriers for unsevered fiber storage or adequate space or retaining means to store excess buffered fiber. In this closure the severed cable may comprise ribbons with splice connectors on the ends of the fibers which must be routed through retaining rings positioned in the base before being directed to the splice platform.
PSI Telecommunications Inc. also markets a Z fiber optics splice closure system for splicing optical fibers which comprises a base and a closure cover with two functional cable ports. Splice storage trays are mounted between side brackets of a footed axial beam with a cross beam to provide cable strain relief. Excess buffered fiber length is coiled about splicing tray edges for storage. Storage of unsevered optical fibers beneath the splice tray is prevented by the axial beam and the interior volume it occupies. No side retaining means for looped unsevered fiber is provided. No means for restricting cable sheath movement is provided. Branch line cables must also enter through the two ports, greatly restricting utility and use for future cable additions.
The closure of the present invention has many advantages over the prior art. It accommodates branch splices readily as it provides storage for unsevered cable.
The closure of the present invention provides an anchor for the strength member and strain relief for the cable adjacent the severed sheath and shield of multiple cables.
The present invention affords expansion to accommodate additional cables for connection to the transmission cable or another cable.